Search Results - (Author, Cooperation:G. N. Geller)

2015-07-24

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; *Biodiversity ; Conservation of Natural Resources/methods ; Ecological Parameter Monitoring/instrumentation/*methods ; Ecology/instrumentation/*methods/standards ; Environmental Policy ; *Satellite Imagery

2013-01-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Alleles ; *Biodiversity ; *Environmental Monitoring ; Genetic Variation ; Population

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract Soil surface temperatures in deserts can reach 70 °C, far exceeding the high-temperature tolerance of most vascular plants of about 55 °C. In this study a computer model indicated that the maximum temperatures of small spherical cacti would approach soil surface temperatures, in agreement with measurements on seedlings of Ferocactus acanthodes. Shortwave radiation was the most important environmental variable affecting maximum cactus temperatures: a 70% reduction in shortwave radiation by shading lowered both predicted and measured stem surface temperatures by 17 °C for plants 2 cm in diameter. High-temperature tolerance, measured as the temperature that halved the fraction of cells taking up a vital stain after a 1 h high-temperature treatment, could reach 60 °C for the detached stems of Opuntia bigelovii, which appears crucial for its vegetative reproduction, and 70 °C for O. ficus-indica, apparently the greatest high-temperature tolerance so far reported for higher vascular plants. Two-fold increases in shortwave absorptance from Epithelantha bokei to Mammillaria lasiacantha to Ariocarpus fissuratus led to a 5 °C predicted increase in maximum temperature. However, compensatory differences in high-temperature tolerances occurred for these dwarf cacti, helping to explain their occurrence in the same open habitat in the Chihuahuan Desert. All six species showed acclimation of their high-temperature tolerance as ambient temperatures were increased, including acclimation by the roots of the dwarf cacti, where the greater sensitivity to high temperatures of roots would exclude them from the upper 2 cm of the soil. Using the model, the observed high-temperature acclimation, and the temperatures needed to reduce stain uptake to zero, the three dwarf cacti were predicted to be able to survive soil surface temperatures of up to 74 °C.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary The temperature and water relations of the largleafed, high-elevation species Frasera speciosa, Balsamorhiza sagittata, and Rumex densiflorus were evaluated in the Medicine Bow Mountains of southeast Wyoming (USA) to determine the influence of leaf size, orientation, and arrangement on transpiration. These species characteristically have low minimum stomatal resistances (〈60 s m-1) and high maximum transpiration rates (〉260 mg m-2s-1 for F. speciosa). Field measurements of leaf and microclimatic parameters were incorporated into a computer simulation using standard energy balance equations which predicted leaf temperature (T leaf) and transpiration for various leaf sizes. Whole-plant transpiration during a day was simulated using field measurements for plants with natural leaf sizes and compared to transpiration rates simulated for plants having identical, but hypothetically smaller (0.5 cm) leaves during a clear day and a typically cloudy day. Although clear-day transpiration for F. speciosa plants with natural size leaves was only 2.0% less per unit leaf area than that predicted for plants with much smaller leaves, daily transpiration of B. sagittata and R. densiflorus plants with natural leaf sizes was 16.1% and 21.1% less, respectively. The predicted influence of a larger leaf size on transpiration for the cloudy day was similar to clear-day results except that F. speciosa had much greater decreases in transpiration (12.7%). The different influences of leaf size on transpiration between the three species was primarily due to major differences in leaf absorptance to solar radiation, orientation, and arrangement which caused large differences in T leaf. Also, simulated increases in leaf size above natural sizes measured in the field resulted in only small additional decreases in predicted transpiration, indicating a leaf size that was nearly optimal for reducing transpiration. These results are discussed in terms of the possible evolution of a larger leaf size in combination with specific leaf absorptances, orientations and arrangements which could act to reduce transpiration for species growing in short-season habitats where the requirement for rapid carbon fixation might necessitate low stomatal resistances.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary The influence of variations in the boundary air layer thickness on transpirtion due to changes in leaf dimension or wind speed was evaluated at a given stomatal resistance (r s) for various combinations of air temperature (T a) and total absorbed solar energy expressed as a fraction of full sunlight (S ffs). Predicted transpiration was found to either increase or decrease for increases in leaf size depending on specific combinations of T a, S ffs, and r s. Major reductions in simulated transpiration with increasing leaf size occurred for shaded, highly reflective, or specially oriented leaves (S ffs=0.1) at relatively high T a when r s was below a critical value of near 500 s m-1. Increases in S ffs and decreases in T a lowered this critical resistance to below 50 s m-1 for S ffs=0.7 and T a=20°C. In contrast, when r s was above this critical value, an increase in leaf dimension (or less wind) resulted in increases in transpiration, especially at high T a and S ffs. For several combinations of T a, S ffs, and r s, transpiration was minimal for a specific leaf size. These theoretical results were compared to field measurements on common desert, alpine, and subalpine plants to evaluate the possible interactions of leaf and environmental parameters that may serve to reduce transpiration in xeric habitats.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary The influence of elevational changes on plant transpiration was evaluated using leaf energy balance equations and well-known elevational changes in the physical parameters that influence water vapor diffusion. Simulated transpirational fluxes for large leaves with low and high stomatal resistances to water vapor diffusion were compared to small leaves with identical stomatal resistances at elevations ranging from sea level to 4 km. The specific influence of various air temperature lapse rates was also tested. Validation of the simulated results was accomplished by comparing actual field measurements taken at a low elevation (300 m) desert site with similar measurements for a high elevation (2,560 m) mountain research site. Close agreement was observed between predicted and measured values of transpiration for the environmental and leaf parameters tested. Substantial increases in solar irradiation and the diffusion coefficient for water vapor in air (D wv) occurred with increasing elevation, while air and leaf temperatures, the water vapor concentration difference between the leaf and air, longwave irradiation, and the thermal conductivity coefficient for heat in air decreased with increasing elevation. These changes resulted in temperatures for sunlit leaves that were further above air temperature at higher elevations, especially for large leaves. For large leaves with low stomatal resistances, transpirational fluxes for low-elevation desert plants were close to those predicted for high-elevation plants even though the sunlit leaf temperatures of these mountain plants were over 10°C cooler. Simulating conditions with a low air temperature lapse rate (0.003° C m-1 and 0.004° C m-1) resulted in predicted transpirational fluxes that were greater than those calculated for the desert site. Transpiration for smaller leaves decreased with elevation for all lapse rates tested (0.003° C m-1 to 0.010° C m-1). However, transpirational fluxes at higher elevations were considerably greater than expected for all leaves, especially larger leaves, due to the strong influence of increased solar heating and a greater D wv. These results are discussed in terms of similarities in leaf structure and plant habit observed among low-elevation desert plants and high-elevation alpine and subalpine plants.

Electronic Resource